1. Department of Anatomy, Physiology and Biochemistry, Biomedical Centre, Swedish University of Agricultural Sciences, SE-751 23 Uppsala, Sweden, Department of Biomedical Sciences and Veterinary Public Health, Swedish University of Agricultural Sciences, SE-750 07 Uppsala, Sweden, and Departamento de Bioquímica y Biología Molecular I and CIBER (Centro Investigación Biomédica en Red) Enfermedades Respiratorias, Universidad Complutense de Madrid, 28040 Madrid, Spain